QuasiModo: Efficient Certificate Validation and Revocation

We present two new schemes for efficient certificate revocation. Our first scheme is a direct improvement on a well-known tree-based variant of the NOVOMODO system of Micali [11]. Our second scheme is a direct improvement on a tree-based variant of a multi-certificate revocation system by Aiello, Lodha, and Ostrovsky [1]. At the core of our schemes is a novel construct termed a QuasiModo tree, which is like a Merkle tree but contains a length-2 chain at the leaves and also directly utilizes interior nodes. This concept is of independent interest, and we believe such trees will have numerous other applications. The idea, while simple, immediately provides a strict improvement in the relevant time and communication complexities over previously published schemes.